Abstarct: Background: Childhood obesity is the result of an imbalance between energy intake and costs of activities. Reduced physical activity and increased consumption of high-calorie diet in the last two decades the main causative factors of obesity and mextabolic syndrome. Physical activity to improve fitness, weight control and reduces the risk factors for mextabolic syndrome. Effect of aerobic exercise with response to weight loss even without weight loss is very importance factor. The aim of this study was to investigate the effect of 8 weeks aerobic training on body composition and mextabolic syndrome indexes in boys under the age of puberty. Method: In this study, 417 students were examined, the number of overweight and obesity were 52 of these students. Relative to the mextabolic syndrome indexes 18 of these students had mextabolic syndrome. These students (age; 10.67± 1.68, weight; 50.44 ± 11.50, BMI; ......) carried out 8 weeks aerobic training. Training program includes: 10-minute warm up, 20 minutes with 50% to 70% of HRmax activities including walking, running, team sport, 20 minutes of football match and 10 minutes cool down. This training program has been done three times a week for 8 weeks. Body composition and blood test including HDL / LDL / CHOL / TG / FBS performed before and after 8 weeks of aerobic training. The WC / WHR also were examined. The results of this study were analyzed using SPSS version 21 for determining changes means paired T-test with significance level was considered. Results: Aerobic exercise causes significant changes in hematological parameters, including triglycerides, systolic blood pressure, heart rate, cholesterol, HDL, fasting blood. No significant changes in other indicators. Conclusions: Application of the selected aerobic program in this study can improve partially of body composition and reducing the risk factors of mextabolic syndrome.